The ability of users to access programs and share data over local area networks (referred to as “LANs”) has become a necessity for most working environments. To improve efficiency and ease of use, certain enhancements may be added to a LAN such as remote wireless access. By providing remote wireless access, a wireless LAN (WLAN) is formed.
As described in U.S. Pat. No. 5,987,062 issued to Netwave Technologies, Inc., now owned by Nortel Networks Limited of Ontario, Canada, one type of WLAN employs dedicated stations, which are referred to as access points (APs). Therein, each AP is a relay station that includes a radio frequency (RF) transceiver that receives radio data packets from a mobile unit (MU) such as a notebook-type computer with a suitable adapter card as described in U.S. Pat. No. 5,987,062. Thereafter, the AP transmits the data packets to the fixed backbone network. Of course, the AP may receive data from the fixed backbone network and transmit it to one or more mobile units.
Before data transmission can occur between the fixed backbone network and an MU by way of an AP, the AP must first authenticate MU. The authentication is accomplished by the MU transmitting a request for authentication message to the AP, and the AP sending back a successful authentication message back to the MU. Once the MU has been authenticated, the MU has to associate itself with the AP. The association is accomplished by the MU transmitting a request for association message to the AP, and the AP sending back in a successful association message. The authentication and association transmission are specified in the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard. Once the MU has been properly authenticated and associated with the AP, then data transmission between the MU and the fixed backbone network can occur.
A problem with current wireless networks deals with the situation where there is significant RF interference in the wireless communications link coupling an AP with the associated MU(s). Typical sources of significant RF interference for wireless network systems include Blue Tooth devices, cellular telephones, microwave ovens, and other devices that transmit RF signals. When significant RF interference is present in the wireless medium of a wireless network system, generally more errors occur in the transmission of data between an AP and the associated MU(s).
The data error of the transmission is not only a function of the RF interference present in the wireless medium, but also of the size of the data packets. In an RF interference free environment, the wireless medium can support the transmission of data packets having relatively long data length without substantial transmission errors occurring. Thus, in an RF interference free environment, the optimal data throughput for the wireless medium occurs when the data packets are at maximum data size, which in a 802.11 compliant wireless network system is 2304 bytes. When RF interference increases in the wireless medium, more transmission data errors occur for the same data packet size. However, if the data packet size is reduced, the transmission data errors can be substantially reduced. Thus, in an RF interference environment, generally there is an optimal data packet size (less than the maximum data packet size) where the data throughput is maximum.
In prior art wireless network systems, a network system administrator occasionally gauges the RF interference present in a wireless network system in order to manually determine the optimal data packet size. This is accomplished by the system administrator causing an AP to send many test patterns to a designated MU with varying data packet sizes, and then measuring the data throughput for each of the data packet sizes. Using this technique, the system administrator can determine the optimal data packet size.
Then, the system administrator manually sets the fragmentation threshold for each AP and MU of the wireless network system above the optimal data packet size. The fragmentation threshold sets the upper limit of the data portion of a packet. That is, if the payload size of a packet is greater than the fragmentation threshold, the data packet is fragmented so that each fragment transmitted has a payload that is less than the threshold. If the payload size of the packet is less than the fragmentation threshold, the packet is not fragmented, and simply transmitted.
The problem with this technique is that RF interference in a wireless environment is typically very dynamic, and therefore, a system administrator cannot practically determine and adjust for the optimal fragmentation threshold for every change in the wireless environment. For example, a person in a business office or a home can turn on the microwave oven for 30 seconds. During that 30-second period, the RF interference in the wireless medium increases. However, it would be impractical or even impossible for a system administrator to gauge the wireless environment for the purposes of determining the optimal fragmentation threshold each time a person turns on a microwave oven or some other RF interference source.
Another problem with current wireless network systems deals with fragmentation threshold as described above, and data transmission using request to send (RTS)/clear to send (CTS). In a 802.11 compliant wireless network system, the AP and the associated MUs are all able to use the wireless medium using carrier sense multiple access with collision avoidance, referred to as CSMA/CA. Using CSMA/CA, an MU first determines if the wireless medium is either idle or busy. If it is idle (i.e. the medium is available for transmission), the MU simply transmits the data packet to the AP, and the AP responds by sending an acknowledgement packet back to the AP if the data packet was successfully received. If the wireless medium is busy, the MU will backoff from sending the data packet for a random time period. After this period, the MU checks the wireless medium again to determine if it is idle or busy.
A problem with CSMA/CA may occur when MUs are within the range of an associated AP, but are outside of each others' ranges. In this case, when the first MU transmits a data packet to the associated AP, the second MU fails to hear that transmission. As a consequences, the second MU may falsely detect that the wireless medium is idle, and transmit its data to the AP, resulting in a collision of the data. The likelihood of this occurring increases when there is a relatively high count of MUs associated with an AP. A system administrator can correct or ameliorate this problem by employing request to send (RTS)/clear to send (CTS) transmissions throughout the wireless network system or at least throughout the sub-system comprising the AP and its associated MUs.
Using request to send (RTS)/clear to send (CTS) transmissions, an MU first sends a request to send (RTS) packet to the associated AP. If the following time slot is already reserved by another MU for transmission of a data packet, the AP simply does not send back a CTS packet. However, if the following time slot has not been reserved for transmission, the AP sends a clear to send (CTS) packet to the transmitting MU indicating that a following time slot is reserved for transmission by the transmitting MU. All other associated MU(s) detecting the CTS packet know that the following time slot is already reserved for transmission by the transmitting MU. Thus, this avoids the problem of MUs being outside the range of each other since the associated MUs will detect the CTS packet sent by the AP.
Typically, request to send (RTS)/clear to send (CTS) transmission are used when there is a relatively high number of MUs associated with an AP. So that request to send (RTS)/clear to send (CTS) transmissions is effective to avoid collisions, it should be enabled for all MUs and associated AP of an AP/MU cluster. However, as alluded to above, a problem with current wireless network systems is that the system administrator has to manually enable each AP and MU when RTS/CTS transmission is desired. Likewise, a system administrator has to enable each AP and MU when fragmentation is desired. Since there can be many APs and MUs in a wireless network system, having a system administrator go around to all of these units to enable RTS/CTS transmissions and/or fragmentation is cumbersome, costly and time-consuming.
Thus, there is a need for a system and method for dynamically controlling a data packet fragmentation threshold in response to changes in network environment conditions, including radio frequency (RF) interference and/or other parameters in a wireless network system. There is also a need for a system and method of globally controlling all MUs (referred to in this application as wireless units (WUs) since they need not be mobile) associated with an AP to enable RTS/CTS transmissions and/or data packet fragmentation. Such systems and methods are provided herein in accordance with the invention.